This invention relates to a rapid blowdown system for a rotary screw air compressor which is integral with an end cap of an air receiver/oil separation tank associated with the compressor, where upon a pressure drop occurring between the suction inlet to the compressor and the air receiver/oil separation tank results in a rapid blowdown of pressure within the air receiver /oil separation tank.
In the past, rotary screw air compressor systems have required a means for rapidly reducing the air pressure within the air receiver/oil separator tank when the compressor operation ceases so as to avoid restarting under a pneumatic load. Typically, in the past the preferred method has been to utilize a pneumatically piloted two-way valve. A conduit typically connecting the valve to the compressor provides a zero or slightly negative gauge pressure to the pilot valve during compressor operation allowing the valve to remain in a closed state. At the instant of compressor cessation, the conduit provides full system pressure to the pilot valve forcing the valve to an open state thereby allowing the system pressure within the compressor tank to be vented through the pilot valve. Generally, the pilot valve has been a separate component of the compressor which can be easily damaged.
It is an object of the present invention, where the compressor is a vehicle mounted compressor, generally driven by suitable drive means from the vehicle engine and having an associated air receiver/oil separation tank remotely located therefrom, to provide a blowdown system which is seamlessly integrated with the air receiver tank housing so as to avoid the dangers associated with accidental damage to such a piloted two-way valve or to associated external hoses and connections.
A further object of this invention is to provide an air receiving tank having an end cap incorporating an integral blowdown system including a blowdown valve having a first end in direct fluid communication with a compressed air receiving tank and a second end in indirect communication with a compressed air receiving tank through a high impedance scavenging orifice which optimally restrict both air and oil flow out of the compressor to the second end of the valve.
It is a further object of the present invention to provide direct fluid communication from both the air receiving tank and the second valve end within the air receiving tank of the compressor, for continuous oil replenishment and pressure equalization.
The present invention is a blowdown system for a rotary screw air compressor, which is integral with an end cap of the air receiving tank. The blowdown system incorporates a generally cylindrical valve housing containing a valve spool. The interior of the valve housing is, at a first end, in fluid communication with an air receiving tank of a compressor through a low impedance first passageway extending from the air receiving tank to the first end of the valve housing. At its second end, the interior of the valve housing is also in fluid communication with the air receiving tank through a second passageway, having a high impedance scavenging orifice at a point of entry to the air receiving tank, the second passageway being in low impedance communication with the air intake or suction line of the compressor. The scavenging orifice provides communication of the interior of the valve housing to the high-pressure end of the compressor. A venting orifice is located at a generally medial point between the first and second ends of the cylindrical valve housing and is selectively closable by sliding a shuttling of the valve spool.
During the operation of the compressor the first passageway, extending from the air receiving tank to the first end of the valve housing, maintains the first end of the valve housing at a system pressure, that is, the air pressure within the air receiving tank and within the interior first end of the valve housing remain identical. The low impedance second passageway provides fluid communication between the second end of the valve housing and the air receiving tank. This second passageway is also in fluid communication with the suction inlet port of the compressor, by way of an air/oil scavenging conduit, which maintains the interior of the second end of the valve housing at a significantly lower pressure, generally near zero or at a slightly negative gauge pressure, that is, a negative pressure relative to local atmospheric pressure. The high impedance scavenging orifice located between the proximal end of the second passageway and the compressed air receiving tank is sized to optimally restrict both air and oil flow out of the air receiving tank. This pressure differential between the first and second end of the valve housing results in the valve being forced toward the second end of the generally cylindrical valve housing during normal compressor operation.
Cessation of compressor operations results in air at system pressure equalizing in both the compressor and the air receiving tank since only minimal loss of pressurized air is possible through the high impedance scavenging orifice. Simultaneously, a mixture of air and oil returns through the air/oil scavenging conduit to the low impedance second passageway and to the interior of the second end of the valve housing. This results in air pressure equalizing at both the first and second ends of the valve housing. A compression spring within the second end of the valve housing then urges the valve spool toward the first end of the valve housing. This action brings the first passageway into communication with a venting aperture to permit rapid decompression of the air receiving tank of the compressor. Suitable annular sealing means adjacent the second end of the valve prevent escapement of compressed air and oil directly from the venting aperture.
In summary, the pressure blowdown system of the present invention for an oil-injected rotary screw air compressor having an output conduit mounted to a high pressure side of the compressor and having a feedback conduit mounted to an intake side of the compressor, includes:
a) a rigid container having a gas reservoir therein, the container having a rigid plate mounted thereon closing the reservoir,
b) a rigid valve housing mounted to the plate, the housing defining a valve spool cavity, the cavity having first and second opposite ends,
c) a valve spool slidably snugly mounted in the cavity for sliding translation between the first and second ends of the cavity, respectively into first and second positions in the cavity.
Resilient means are mounted in the cavity for resiliently urging the valve spool from the first end towards the second end of the cavity.
A first gas passageway in the plate provides unobstructed fluid communication between the first end of the cavity and the feedback conduit of the compressor. A second gas passageway in the plate provides unobstructed fluid communication between the second end of the cavity and the gas reservoir, where the gas reservoir is in unobstructed fluid communication with the output conduit of the compressor.
The valve housing has an exhaust aperture into the cavity so that the cavity is in fluid communication with ambient atmosphere when the exhaust aperture is not closed by the valve spool. The exhaust aperture is positioned so as to be covered by the spool when the spool is translated into the first the second position in the cavity. The spool has a third gas passageway therethrough in fluid communication from the second end of the cavity to the exhaust aperture when the spool is in the second position. The spool when not in the second position seals the exhaust aperture closed.
A fourth gas passageway may be provided which is in fluid communication between the gas reservoir and the first gas passageway. The fourth gas passageway contains a flow restricting orifice therein restricting fluid flow between the gas reservoir and the first gas passageway.
A second end-exposed face of the spool, which faces the second end of the cavity, includes a spacing protrusion extending therefrom along a shuttle axis of the spool for spacing the second end-exposed face from an end wall of the second end of the cavity when the spool is in the second position. A first end-exposed face of the spool opposite the second end-exposed face may include a bayonet mount mounted thereto and aligned along the shuttle axis. The resilient means may be a helical spring. The plate may be an end cap on the container.
The valve spool and the cavity may be cylindrical and the second gas passageway may include an annular channel formed around the spool. A bore may extend from the second end-exposed face of the spool to the annular channel. The annular channel extends annularly around the shuttle axis of the spool and aligns with the exhaust aperture when the spool is in the second position.
A fifth gas passageway may be provided in the plate in fluid communication between the gas reservoir and a pressure signal line extending between an inlet valve of the compressor and the fifth gas passageway.
The plate may be mounted to the container so as to extend between a bottom of the container adjacent the bottom of the gas reservoir and a top of the container. The second gas passageway may be located adjacent the top of the gas reservoir.
The fourth gas passageway may be located at the bottom of the gas reservoir. The first gas passageway may intersect the fourth gas passageway at the bottom of the gas reservoir and the feedback conduit may be mounted to the first gas passageway at the bottom of the gas reservoir.